[PATCH] D154205: [MachineLICM] Handle subloops

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

In D154205#4494166 <https://reviews.llvm.org/D154205#4494166>, @craig.topper wrote:

> My question wasn't about visiting the inner loops it was about the order of visiting. Since I think it visits all blocks in child loops, I was wondering if we could aggressively hoist everything relative to the outer loop first instead of gradually. Then visit the inner loops to get anything that can't be hoisted all the way out. Though if we do as @nikic says and stop visiting blocks of inner loops when visiting outer loops, this won't work.

There are multiple ways to go about this. We could only visit the outermost loop, but hoist to an inner loop preheader while doing so (i.e. perform the invariance check against the current inner-most loop to find candidates, and then hoist them to the outer-most parent loop that is still invariant). It's possible that doing this fits better into the MachineLICM model, which also needs to keep track of register pressure.


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